Tecnai t12 biotwin tem

For imaging Luc-QD conjugates, glow-discharged carbon-coated 400 mesh copper grids (Electron Microscopy Science) either unstained or negatively stained with 0.75% uranyl formate solution were used. For cell imaging, at 30 min after CTZ injection CT-26 cells were fixed with 3% glutaraldehyde in 0.1 M cacodylate buffer (pH 7.2) containing 0.1% CaCl₂ for 2 h at room temperature. The cells were washed five times with 0.1 M cacodylate buffer at 4 °C and then post-fixed with 1% OsO₄ in 0.1 M cacodylate buffer containing 0.1% CaCl₂ for 2 h at 4 °C. After rinsing with cold distilled water, the cells were dehydrated slowly with a series of ethanol and propylene oxide at 4 °C. Then, the samples were embedded in Embed 812 resin (Electron Microscopy Science). After polymerization at 70 °C for 36 h, serial sections were cut by an ultramicrotome (Ultracut UC7, Leica) and mounted on formvar-coated slot grids (Electron Microscopy Science). The sections were stained with 4% uranyl acetate for 10 min and lead citrate for 7 min. Images were recorded with a FEI Tecnai T12 Bio-TWIN TEM operated at 120 kV with a 67,000× or 110,000× nominal magnification.